The present invention relates to a method for controlling a driving distance between a host vehicle and a first vehicle driving in front of said host vehicle, said host vehicle driving at a driving speed and at said driving distance to said first vehicle, said host vehicle comprising: a system for controlling said driving distance, which is adapted to retain said driving distance at not less than a minimum safety distance, and a fuel saving system, which includes an automatic speed increasing function, which automatic speed increasing function, upon fulfilment of a set of conditions, is activated to automatically increase the driving speed in order to utilise the kinetic energy inherent in said host vehicle to save fuel.
Fuel saving systems in general are known. In particular, fuel saving systems might define situations where a speed increase of the vehicle is suitable in order to save fuel by utilising the kinetic energy inherent in the vehicle. To determine where such situations will occur, the fuel saving systems may include systems in which the road ahead of a vehicle is surveyed in order to take information on the gradient of the road ahead into account, when operating the speed of the vehicle.
The gradient of the road may be taken into account using different conditions as set by the vehicle manufacturer. For example, one set of conditions may include the detection of a downhill route ahead of the vehicle, in which downhill the vehicle is allowed to increase speed beyond a set speed limit through i.a. freewheeling. Another set of conditions may instead include the detection of an upcoming uphill, where the vehicle is allowed to increase speed before reaching the climb. The vehicle consequently gains extra momentum at a position, on the road where such extra momentum is low-priced in terms of fuel economy. When reaching the climb the extra momentum is used to, at least to a certain extent, assist the vehicle to reach the top of the hill without too much effort and without losing too much speed during climbing.
Vehicles may also be provided with cruise control functionality which controls the speed of the vehicle and, more recently, optionally controls a minimum safety distance to a lead vehicle ahead of the vehicle in question. The safety distance may also be controlled by the aid of a system separated from the cruise control.
The industry strives continuously to reduce fuel consumption. It is desirable to further improve fuel consumption of vehicles provided with systems such as the ones described above, or to provide a useful alternative.
According to one aspect of the present invention, a method for controlling a driving distance between a host vehicle and a first vehicle driving in front of said host vehicle is disclosed, said host vehicle driving at a driving speed and at said driving distance to said first vehicle. Said host vehicle comprises:
a system for controlling said driving distance, which is adapted to retain said driving distance at not less than a minimum safety distance, and
a fuel saving system, which includes an automatic speed increasing function, which automatic speed increasing function, upon fulfilment of a set of conditions, is activated to automatically increase the driving speed in order to utilise the kinetic energy inherent in said host vehicle (H) to save fuel.
The method comprises the steps of:
retrieving information to prepare for activation of said automatic speed increasing function,
preparing for said activation by
setting the minimum safety distance to a first distance, whereby, when said driving distance is less than said first distance, said system for controlling the driving distance will adapt said driving speed until said first safety distance is reached,
allowing activation of the automatic speed increasing function only when, the driving distance is at least said first distance, and upon retrieval of information that said set of conditions is fulfilled,
and, upon activation of said automatic speed increasing function, setting the minimum safety distance to a second distance, said second distance being shorter than the first distance,
such that the difference between the second and the first distances is available during the activity of the speed increasing function to perform an automatic speed increase without conflict with the system for controlling a driving distance.
The inventive method is aiming at reducing fuel consumption for the vehicle. This is achieved by an improved cooperation between the fuel saving system and the system for controlling said driving distance. The two systems may otherwise obstruct one another, such that the system for controlling the driving distance counteracts the fuel saving system. For example, when a freewheeling function of the fuel saving system is launched in order to utilise the kinetic energy inherent in the vehicle, a pre-set minimum safety distance of the system for controlling driving distance between the host vehicle and a first or lead vehicle may be reached, and the vehicle, i.e. the host vehicle, is slowed down by the system for controlling driving distance. The slowdown may be achieved in several ways, such as utilising the vehicle brakes, disengaging the freewheeling function, or otherwise. Under such conditions the fuel saving prospect is reduced.
Instead, according to the present invention, the minimum safety distance used by the system for controlling driving distance is set to a first distance in preparation for activation of the speed increasing function. Moreover, the conditions are set that the driving distance must be at least said first distance, and information that the set of conditions for the automatic speed increase is fulfilled must be retrieved, in order for the automatic speed increase function to be activated (launched). Hence, the minimum safety distance used by the system for controlling driving distance will be set to a first distance before the automatic speed increasing function may be activated. Accordingly, before the automatic speed increasing function is activated, the vehicle is adapting its driving speed until the first distance to the first vehicle is reached.
When the first distance is reached, the automatic speed increasing function is allowed to be activated, and hence it may be activated if the set of conditions is fulfilled. The set of conditions could advantageously include conditions being obtained by automatic systems connected to the vehicle, but optionally one set of conditions could also include a decision of a user.
When the automatic speed increasing function is activated, the minimum safety distance is set to a second distance, being shorter than said first distance. In other words, the minimum safety distance is altered by the difference between the second distance and the first distance. This provides the vehicle with an adequate distance (said difference) to a first vehicle to make use of its automatic speed increasing function without conflict with the system for controlling driving distance. Thereby, fuel may be saved by utilising the inherent kinetic energy of the vehicle.
Advantageously, the second distance may be set so as to be satisfying in view of safety reasons, such that the host vehicle and the first vehicle are kept separated by an adequate driving distance. Hence, safety need not be compromised when using the fuel saving function.
A vehicle according to the present invention may be any one of a lorry or truck, a passenger car or bus, or any other vehicle for which such methods are appropriate. The words lorry and truck are meant both to represent a heavy-duty vehicle of any size and may be used interchangeably. The system for controlling said driving distance and the fuel saving system may be integrated into a single system if found appropriate. The distances as encompassed in the present invention may be calculated either as a distance in time or in length if nothing else is specified. A distance between two vehicles may be a distance from a front end of a host vehicle and a rear end of a first vehicle. However alternatives, such as front end to front end, may apply if found appropriate and depending on the systems for monitoring such distances present in the vehicles in question. The adaption of driving speed of the host vehicle may be achieved in several ways, such as by freewheeling, by reducing motor torque to the vehicle wheels, and by utilising vehicle brakes in combination with any energy retrieval functionality. It is however preferable if this adaptation is achieved in a fuel consumption beneficial way. The set of conditions to be fulfilled may include one or several conditions set by the vehicle manufacturer and include current speed and current speed limits, road curvature in both horizontal and vertical direction, and whether conditions influencing the road driveability.
In certain embodiments the fuel saving system may be a system whose function is selectable by a user. That is, the fuel saving system might not be running by default but a user-initiated activation must be performed for the fuel saving system to be active. In this case, preferably, a driver-initiated activation may be performed for activating the fuel saving system. In practice, this means that the driver could, for example by means of a dedicated button, select whether the fuel saving system shall be on or off.
In other embodiments, the fuel saving system may always be running by default.
In certain, embodiments, information to prepare for activation of the automatic speed increasing function is always available when the fuel saving system is active. Hence, whenever the fuel saving system is running, the preparation for said activation takes place by setting the minimum safety distance to a first distance, and by determining that the automatic speed increasing function may only be allowed if the driving distance is at least said first distance.
However, in preferred embodiments, the information to prepare for activation of the automatic speed increasing function is available only when the fuel saving system is active and said set of conditions of the automatic speed increasing function is about to be or is fulfilled. Accordingly, in this case the preparation for said activation will take place only when the system estimates that a situation where the automatic speed, increasing function shall be used is approaching. For example, in a vehicle surveying the curvature of the road ahead, the presence of a downhill slope ahead of the vehicle may indicate that the set of conditions is about to be fulfilled. Hence, when the downhill slope ahead of the vehicle is detected, the preparation for activation of the speed increasing function takes place, whereby the distance to the first vehicle will, be increased to the first distance. When the first distance is reached, and when the vehicle reaches the downhill slope, the automatic speed increasing function will be launched, and the minimum driving distance be set to the second distance, such that the difference distance may be used by the speed increasing function.
Advantageously, the system for controlling said driving distance includes a preset minimum safety distance, and the first distance may be set by adding an offset distance to the pre-set minimum safety distance.
In this case, the second distance may advantageously be equal to the pre-set minimum, safety distance, such that the offset distance is available during the activity of the speed increasing function.
This alternative has the advantage that the driver will recognise that the pre-set minimum safety distance is never shortened. In many systems, the pre-set minimum safety distance may be selected by the driver, hence reflecting his/her own requirements.
Alternatively, the system for controlling said driving distance includes a pre-set minimum safety distance, and the first distance equals to the pre-set minimum safety distance.
According to one embodiment the difference between said second distance and said first distance, in certain embodiments being the offset distance, is dependent on the driving speed. Hence the altered safety distance is also dependent on the driving speed.
Consequently, the safety level may be adapted depending on the driving speed, such as i.a. when driving at a lower speed the distance to a lead vehicle may be shorter by setting a shorter offset distance, although the safety level may still be kept at a reasonably high level.
According to one embodiment said host vehicle further comprises an active cruise control system, whereby the method further comprises:
driving at said driving speed under control by said active cruise control system.
According to one embodiment said host vehicle comprises freewheeling means whereby a propulsion unit may be disconnected from driving wheels of said host vehicle, wherein the step of activating said automatic speed increasing function includes launching of said freewheeling means.
According to one embodiment the step of retrieving information that said set of conditions is or is about to be fulfilled includes:                monitoring whether said set of conditions is fulfilled, and/or communicating information that said set of conditions is fulfilled.        
Either the fuel saving system itself comprises monitoring functionality for monitoring the set of conditions, or the fulfilment of said set of conditions is communicated to it.
According to one embodiment the step of adapting said driving speed until said first distance is reached includes:
monitoring a topography of an intended drive ahead of the host vehicle, and selecting a position along said monitored intended drive for the step of adapting said driving speed until said altered safety distance is reached, in which position a favourable fuel consumption for the host vehicle is achieved for performing said step.
Hereby a monitored drive ahead of the vehicle may fulfil the set of conditions such that the automatic speed increasing function is allowable, but the activation thereof is postponed. The inventive method encompasses the selection of a position for activation of the automatic speed function for which favourable fuel consumption, i.e. possibly even more favourable fuel consumption, is achieved.
According to one embodiment the step of monitoring whether said set of conditions is fulfilled includes:
monitoring a topography of an intended drive ahead of the host, vehicle, and evaluating whether said intended drive includes an uphill slope which fulfils said set of conditions such that said automatic speed increasing function is enabled with the intention of increasing speed in advance of said uphill slope such that fuel may be saved during climbing thereof.
The climbing of an uphill slope may be fuel consumption intense, and the fuel consumption may be reduced if the inventive method is adapted to take such slopes into account when activating the automatic speed increasing function.
According to one embodiment the step of monitoring a topography of an intended drive ahead of the host vehicle includes using a Global Positioning System (GPS).
According to one embodiment the step of monitoring said set of conditions includes:                monitoring a topography of an intended drive ahead of the host vehicle by the aid of a Global Positioning System (GPS), and        calculating along said intended drive whether said set of conditions is fulfilled.        
According to one embodiment the step adapting said driving speed until said first distance is reached and/or of monitoring whether said set of conditions is fulfilled includes:                assessing a near future behaviour of said first vehicle, preferably by estimating a weight/power ratio thereof.        
By taking the near future behaviour of a first vehicle into account, or at least trying to take such behaviour into account, even more reduced fuel consumption may be achieved. By estimating e.g. a weight/power ratio of a first vehicle, it may be possible to predict, at least to a certain degree, its driving behaviour on the intended drive ahead such that the likelihood of a slowdown of the first vehicle. Other prediction measures may be contemplated, such as vehicle type, or driving style of the driver of the first vehicle.
According to one embodiment, the monitoring of a topography of an intended drive and/or the assessment of a near future behaviour of the first vehicle is used as input for selecting the difference between the second and the first distances, so as to adapt said difference to an estimated upcoming situation.
According to one embodiment the step of adapting said driving speed until said altered safety distance is reached includes automatically reducing power output to said driving wheels.